The invention generally relates to a method and apparatus for manufacturing metallic parts, and more particularly to a method and apparatus for manufacturing metallic parts by a process involving injection of a melted metal into a mold.
One method used to produce molded metallic parts from melted metal is by die casting. One die casting system and method are described in U.S. Pat. No. 5,983,976, hereby incorporated by reference. Die casting methods inject liquid metal into a mold.
Semi-solid methods for producing molded metallic parts differ from the die casting methods by injection molding a metal in its semi-solid state rather than in its liquid state. Semi-solid injection molding systems and methods are disclosed in U.S. Pat. Nos. 5,836,372 and 6,135,196, both of which are incorporated by reference herein.
The die casting system described in U.S. Pat. No. 5,983,976 is illustrated in FIG. 1. The system 10 includes an injection molding apparatus 10 and a mold 14. Apparatus 10 is preferably mounted on wheels and/or rails (not shown) such that it may be retracted from the mold 14 after each injection step and advanced toward the mold 14 before each injection step by a motor or hydraulics (not shown).
The apparatus 10 contains a melt feeder 23 provided with at least one heating element 25 disposed around its outer periphery. The feeder 23 is mounted on an inclined temperature-controlled metering barrel 30 such that the liquid metal flows from the feeder 23 to barrel 30 by way of gravity through a feeder conduit or port 27. A ram or metering rod 32 is arranged coaxially with the barrel 30 and extends along the center axis of the barrel 30. The ram 32 is controlled by motor 33 for axial movement in both retracting and advancing directions along the barrel 30 to meter the amount of metal leaving barrel 30 and for rotation around its own axis if stirring of the melted metal is desired inside barrel 30. The motor 33 is mounted on the upper end of barrel 30.
The metering barrel 30 is mounted over an injection or accumulation barrel 50. The metering barrel 30 is mounted above the injection barrel 50 such that it is inclined with respect to the horizontal direction. An inlet port or conduit 37 is located between the barrels through which the metal flows between the metering barrel 30 and injection barrel 50.
The injection barrel 50 contains a plunger or piston 45 and an injection nozzle 57. The plunger 45 contains a seal, such as O-ring(s) 41, to form an air tight seal with the inner surface of the injection chamber 50. The plunger 45 is advanced in the injection chamber 50 by a motor or hydraulics (not shown) to inject the liquid or semi-solid metal from the injection chamber 50 through the nozzle 57 into a mold cavity 13 in mold 14. The apparatus 10 produces high quality injection molded parts at a low cost. The remaining elements shown in FIG. 1 are described in U.S. Pat. No. 5,983,976.
However, the present inventor has noted several problems with the apparatus 10 which increase the apparatus maintenance costs and down time. First, the liquid metal in the metering barrel 30 seeps into the motor 33, which requires increased maintenance of the motor. Second, the bolts which connect barrel 30 to barrel 50 need frequent replacement due to the stress placed on the bolts by the weight of the metering barrel.
According to one preferred aspect of the present invention, there is provided an injection molding apparatus, comprising an injection chamber located in a first plane and mounted over a base of the apparatus, a metering chamber located at least partially above the first plane, and in fluid communication with the injection chamber, a metering element located in the metering chamber, a first driving mechanism which moves the metering element, wherein the first driving mechanism is connected to the metering chamber, and a melt feeder in fluid communication with the metering chamber. A fill line of the melt feeder is located below a first opening between the metering chamber and the first driving mechanism, and/or the melt feeder is mounted to the base of the apparatus.
According to another preferred aspect of the present invention, there is provided a metal injection molding apparatus, comprising a first means for housing metal to be injected into a mold, the first means located a first plane and mounted over a base of the apparatus, a second means for housing the metal to be metered, the second means located at least partially above the first plane, a third means for metering metal into the first means, a fourth means for moving the third means, and a fifth means for melting the metal provided into the second means, such that melted metal in the fifth means is located below a first opening between the second means and the fourth means and/or the fifth means is mounted to the base of the apparatus.
According to another preferred aspect of the present invention, there is provided a metal injection molding method, comprising providing solid metal into a melt feeder, melting the solid metal into a liquid state, such that fill line of the liquid metal is below a first opening between an inclined metering chamber and a first driving mechanism, providing the liquid metal into the inclined metering chamber containing the first driving mechanism attached to an upper portion of the metering chamber, metering the metal from the metering chamber into an injection chamber located below a lower portion of the metering chamber, and injecting the metal from the injection chamber into a mold.